Previous reports describe induction of the differentiation of immature hepatocytes and the functional maintenance of the differentiated hepatocytes using in vitro cell culture methods such as 2D culture, 3D culture, and coculture. Such hepatocytes differentiated in vitro, however, are difficult to maintain functionally, as compared with in vivo adult hepatocytes. On the other hand, human adult hepatocytes are poorly proliferative and scarcely available and are therefore difficult to supply in large quantities to the pharmaceutical industry.
Mercer, Mukaidani, et al. have reported that when cryopreserved human hepatocytes were transplanted into immunodeficient mice with liver damage (uPA-Tg/scid), approximately 50 to 70% of the liver was replaced with human hepatocytes in vivo (Non Patent Literature 1: Nat Med 7: 927-933, 2001; and Patent Literature 1: WO2003/080821). Nonetheless, the production of chimeric mice having human-derived hepatocytes from the uPA-Tg/scid mice is still insufficient means for large-scale proliferation of human hepatocytes, though the chimeric mice can be useful in themselves. In addition, the human hepatocyte-transplanted chimeric mice are incapable of long-term survival (shorter than 50 days) and mouse hepatocytes proliferate in the course of growth, so their applicability to systems for in vivo evaluation of toxicity against or drug efficacy for human hepatocytes is limited.
In addition, Su et al. have reported that in a transplantation of human hepatocytes into a Fah−/−NOD/scid model, the replacement with human hepatocytes was approximately 33.6% at maximum (Non Patent Literature 2: Sci China Life Sci 54: 227-234, 2011). Bissing et al. have reported that in a transplantation using Fah−/−/Rag2−/−/Il2rg−/− triple KO mice, the replacement with human hepatocytes was approximately 20% at maximum (Non Patent Literature 3: Proc Natl Acad Sci 104(51): 20507-20511, 2007). Immunodeficient TRECK mice, which are transgenic mice developed by Saito et al., express a diphtheria toxin receptor human HB-EGF in particular cells and permit specific ablation of target cells through the administration of diphtheria toxin at any stage of time course (Non Patent Literature 4: Nat Biotechnol.; 19(8): 746-50, 2001). Also, Matsumoto et al. have reported that a transplantation of mouse fetal hepatocytes into TRECK-based hepatitis model mice (Alb-TRECK) improved the rate of their survival (Non Patent Literature 5: Transplantation; 84(10): 1233-9, 2007). Ishii et al. have reported that a transplantation of hepatocytes derived from mouse embryonic stem cells into immunodeficient Alb-TRECK mice improved the rate of 35-day survival (Non Patent Literature 6: Stem Cells. 25(12): 3252-60, 2007). Matsuoka et al. have reported that human albumin was detected in blood when human adult hepatocytes were transplanted into immunodeficient Alb-TRECK mice (Non Patent Literature 7: “Method for producing human liver-chimerized Tg mice” Hiromichi Yonekawa, Kunie Matsuoka, The Tokyo Metropolitan Institute of Medical Science/disease model development center, the 7th research exchange forum, 2008 Feb. 27, Tokyo, Japan).